1. Field of the Invention
The present invention relates to an object determining apparatus, and more particularly to a object determining apparatus for use with a vehicle for determining whether an object in front of the vehicle is a three-dimensional object or a road surface.
2. Description of the Related Art
There has been conventionally known a external monitoring apparatus for a vehicle that differentiates road and three-dimensional objects on the basis of a height from a road surface (Japanese Patent Application Laid-Open (JP-A) No. 5-265547). In the case of detecting the road by the vehicle external monitoring apparatus, distance data close to the road surface (low height) is selected and by using a road model the road shape is detected. However, in order to detect a three-dimensional object, disparity points in which a height from the road surface is 10 cm or less is deleted from the previously found disparity points. Further, a histogram of the number of the disparity points is derived per lattice in which the disparity and the image width are fixed (in which a disparity resolution is 1, and an image has a width of 4 pixels), and a maximum value thereof is selected as data of a three-dimensional object.
Further, there has been proposed a plane estimating method for recognizing ground surfaces as a flat surfaces by globally approximating ground surfaces having few features, such as the road surface, the floor and the like, to flat surfaces (JP-A No. 9-81755). In this plane estimating method, a linear approximation is executed by finding the correspondence of blocks of m pixels×n pixels, finding a distance (a disparity point), picking up blocks in which a vertical position (iY) of the image exists within a common region, and using the blocks having the correspondence. A distance is interpolated with respect to the blocks having no correspondence by executing the linear approximation. Further, the road surface is detected by executing the linear approximation while changing the vertical position (iY) of the image, and executing an estimation of the plane in the entire image after the linear approximation is finished at all the vertical positions (iY) of the images.
However, in the prior art disclosed in JP-A No. 5-265547, since the road surface model is prepared by detecting the distance data close to the road surface, the distance data close to the road surface can not be detected in the case where a white line or the like does not exist on the road surface, giving cases where the road surface model can not be prepared. In the technique disclosed in JP-A No. 9-81755, it is possible to employ the technique even when the number of road patterns is small. However, since the road surface is globally approximated, there is a problem that a passenger standing on the road surface may be regarded as the plane.
Further, since the prior art employs blocks defined by fixed disparity intervals and image lateral position intervals, the size of the width of one element in a map becomes non-uniform with the distance and size in three-dimensional coordinates of real space. Therefore, since object are determined by a maximum value of the disparity and the votes of the disparity points to the map, there is a problem that it is hard to accurately determine the object.